$(function(){
$('#form').submit(function(){
alert('Thanks!');
});
});
<body>
<form action="javascript:;" id="form">
<h3>Please fill in a german zip code (5 numbers)!</h3>
<input pattern="\d{5}" required="required" id="input" />
<input type="submit">
</form>
</body>
input:focus {
background-color: green;
}
input:focus:invalid {
background-color: red;
}
* {
overflow: hidden;
}